In recent years there has been a pronounced effort to produce superior lubricants. Attempts to make such superior lubricant materials have revolved around improved refining of natural mineral oil base stocks and the creation of new synthetic base stocks which have good basic lubricity characteristics. Where new compounds were synthesized, there were attempts made to produce compounds which had known oxidation resistant sites, such as quaternary carbon atoms. Additionally, it was attempted to produce long chain hydrocarbon compounds, since it was known from mineral oil technology, that long chain hydrocarbons had both good lubricity and good smoke points. Although long chain aliphatic groups have good lubricating properties, they usually also have relatively high freeze and cloud points.
Thus, many synthetic lubricants are based on decene oligomers because these compounds have an excellent combination of properties including long aliphatic chains, which provide good slipperiness, relatively low freeze and cloud points, and oxidation resistant loci in the same molecules.
Recently, it has been found, by one of the inventors of the subject matter hereof, that decenes which have been oligomerized over Group VI B metal catalysts, particularly reduced chromium catalysts, produce unusually fine lubricant base stocks. The products of this oligomerization tend to have very uniform molecular structure, low branch ratios and low pour points. Fine synthetic lubricants and viscosity index (V I) improvers have been formulated from these decene oligomers, which are principally trimers. Reference is here made to U.S. Pat. Nos. 4,827,064 and 4,827,073, issued in the name of one of the inventors hereof, which show the novel production of excellent alpha olefin oligomers which find utility in the lubricant field.
Alkyl aromatics are very well known organic compounds. They have a wide variety of known uses in detergent and lubricant technologies, and they have been used as precursors for producing over-based aryl sulfonates.
In general, alkyl aromatics have usually been made by alkylating existing, preformed aromatic compounds, such as benzene, toluene, xylene, naphthalene, etc., with alpha olefins. There has recently arisen an interest in finding alkyl aromatics which would be useful in lubricant formulations. Inherently, these materials should make good lubricant base stocks because they have long alkyl chains to provide the needed lubricity characteristics, and aromatic nuclei which should provide good oxidation resistance and solvency for polar additives, such as antiwear additives, antioxidants, etc. Further, their molecular structure is such that these molecules should have relatively low freeze and cloud points.
Alkyl aromatics are commercially available materials. They are conventionally synthesized by the direct addition of olefins, particularly alpha olefins, to aromatic nuclei, particularly benzene. This reaction is known to produce a mixture of mono and multi substituted benzenes in which the alkyl groups may be straight or branched chain. Indeed, some of the alkyl substituents may be straight chain and others may be branched chain in the same molecule.
Reference is here made to an article by K. C. Eapen et al. Poly-normal-alkylbenzene Compounds: A Class of Thermally Stable and Wide Liquid Range Fluids: Preprints of the Division of Petroleum Chemistry, No. 4, pages 1053-1058 American Chemical Society, Philadelphia Meeting, Aug. 26-31, 1984. This article reviews the state of the art relative to making alkyl aromatic compounds for use as lubricants, as well as a review of the properties of such lubricants as have been made with these base stocks. It is well known, from conventional inorganic chemistry, that reactions requiring stoichiometric quantities of Grignard reagents as described in this reference, are difficult and expensive to run. Further, it is known that this type of reaction is difficult to control in that the amount of alkylation and the particular position of the alkyl substitution may not always be exactly where it is most desired that it be. As a result, while the reaction may be generally known, the production of reaction products which are suited to use as lubricants is in no way shown by this reference, nor is it possible to use this stoichiometric Grignard reagent reaction to produce lubricant quality products.
In this art, it is to be noted that the lubricant base stock is often the whole reaction product, or at least a substantial portion thereof, with a minimum of product purification. It is most unusual for a pure compound or compounds to be used as a lubricant base stock because the cost of isolation of a pure compound would be so significant that the product so produced might well be priced out of the market almost regardless of the properties that it possessed. Thus, the lubricant base stock which is actually used is usually a mixed reaction product which has been refined to the least extent possible consistent with obtaining the properties which are desired.